Declared Distances in Airport Planning

Declared distances are fundamental, standardized values in airport design, flight operations, and regulatory compliance. They define the portions of runway and associated areas that are formally available for takeoff and landing, and they are critical for ensuring safe and predictable operations for all aircraft types.

What Are Declared Distances?

Declared distances refer to the published runway length values for each runway direction at an airport. These values account for operational and safety considerations—such as obstacles, pavement strength, and runway safety areas—and are specified by the airport operator, with oversight and approval by national aviation authorities (such as the FAA or those in other ICAO member states). Declared distances are always published in official aeronautical sources and are legally binding for aircraft performance planning.

The four main types of declared distances are:

• TORA (Takeoff Run Available)
• TODA (Takeoff Distance Available)
• ASDA (Accelerate-Stop Distance Available)
• LDA (Landing Distance Available)

Each of these serves a distinct role in aircraft performance calculations and operational planning.

The Four Main Declared Distances

Takeoff Run Available (TORA)

TORA is the length of runway declared suitable and available for the ground run of an aircraft during takeoff.

• Definition: The portion of the runway, starting at the threshold, available for the takeoff roll.
• Use in operations: Pilots use TORA to ensure their calculated ground run distance does not exceed the available runway.
• Limitations: TORA may be less than the physical runway if some sections are reserved for safety areas or are not suitable for takeoff.
• Regulatory references: ICAO Annex 14, FAA Advisory Circular 150/5300-13B.

Example:
A runway is 3,000 meters long, but 200 meters at the beginning are reserved for a Runway Safety Area. The published TORA is 2,800 meters.

Takeoff Distance Available (TODA)

TODA is the total length available for the takeoff run plus any clearway, which is a defined area beyond the runway that is free of obstacles and suitable for aircraft to overfly during initial climb.

• Definition: TORA + length of clearway
• Use in operations: Certain aircraft, if permitted by their certification and regulations, may use the clearway to extend their takeoff performance.
• Limitations: Not all aircraft or types of operations allow use of clearway in takeoff calculations. Only officially declared clearways count toward TODA.

Example:
TORA is 2,500 meters, clearway is 250 meters, so TODA is 2,750 meters.

Accelerate-Stop Distance Available (ASDA)

ASDA is the length of runway plus any stopway declared available for an aircraft to accelerate to decision speed (V1), then abort and come to a complete stop.

• Definition: TORA + length of stopway
• Use in operations: Pilots use ASDA to ensure the aircraft can safely abort the takeoff and stop within the available distance.
• Limitations: Stopways must be constructed and maintained to support aircraft in an aborted takeoff; only officially declared stopways are included.

Example:
Runway is 3,000 meters with a 200-meter stopway: ASDA is 3,200 meters.

Landing Distance Available (LDA)

LDA is the length of runway declared available and suitable for landing, measured from the landing threshold to the end of the runway.

• Definition: The portion of the runway available for landing roll, starting at the threshold (which may be displaced).
• Use in operations: Pilots must ensure their calculated landing distance does not exceed the LDA.
• Limitations: LDA is reduced by displaced thresholds, obstacles, or pavement limitations; it does not include stopways or clearways.

Example:
Runway is 3,000 meters with a 300-meter displaced threshold; LDA is 2,700 meters.

Supporting Terms and Features

Clearway

A clearway is a rectangular area beyond the runway, under airport control, free from obstacles and suitable for aircraft to overfly during takeoff (but not to roll on).

• Purpose: Extends TODA for eligible aircraft.
• Markings: Often marked with yellow chevrons.
• Limitations: Not all aircraft are permitted to use clearway in their takeoff calculations.

Stopway

A stopway is an area at the end of the runway, aligned with the runway, able to support the aircraft during an aborted takeoff.

• Purpose: Extends ASDA, providing a safety margin for rejected takeoffs.
• Markings: Marked with yellow chevrons, indicating not for routine use.
• Limitations: Not for taxi, takeoff, or landing except in an aborted takeoff.

Displaced Threshold

A displaced threshold is a threshold located at a point other than the physical beginning of the runway. The area before the threshold may be used for taxi, takeoff, or rollout, but not for landing touchdown.

• Purpose: Improves obstacle clearance or protects pavement.
• Effect: Reduces LDA.

Runway Safety Area (RSA)

The Runway Safety Area is a surface surrounding the runway, prepared to minimize damage to aircraft in case of undershoot, overshoot, or excursion.

• Purpose: Enhances safety; may reduce declared distances if not compliant.
• Regulation: Dimensions based on aircraft and runway type.

Runway Protection Zone (RPZ)

The Runway Protection Zone is an area beyond the runway end, intended to protect people and property on the ground.

• Purpose: Maintains safety for ground areas; may influence placement of thresholds and declared distances.

Why Are Declared Distances So Important?

• Safety: They ensure that only the portions of the runway and associated areas that meet regulatory, geometric, and obstacle clearance requirements are used for takeoff and landing.
• Regulatory Compliance: Only declared distances may be used in official aircraft performance calculations; using more or less is a violation.
• Operational Planning: Pilots, dispatchers, and airport operators rely on these values to determine if aircraft can safely operate under specific conditions.

How Are Declared Distances Published?

Declared distances are published in:

• National Aeronautical Information Publications (AIPs)
• FAA Chart Supplements (U.S.)
• Airport diagrams and NOTAMs
• Commercial charts (e.g., Jeppesen), though the official operator’s figures take precedence

Pilots and operators must always reference the most current official publications for declared distances.

Application in Flight Planning and Operations

During preflight planning and aircraft performance calculations:

• Takeoff: The calculated takeoff run, distance, and accelerate-stop distance required must not exceed the published TORA, TODA, or ASDA.
• Landing: The landing distance required must not exceed the published LDA.
• Abnormal Operations: Safety margins depend on declared distances being observed in emergencies or abnormal procedures.
• Compliance: Exceeding declared distances or using unofficial values is a regulatory violation and a serious safety risk.

Frequently Asked Questions

Q: What are the four main types of declared distances?
A: TORA, TODA, ASDA, and LDA—each essential for different aspects of aircraft performance and airport design.

Q: Why might declared distances be less than the physical runway length?
A: Due to displaced thresholds, obstacles, safety areas, pavement strength, or construction; only the officially declared portion is usable.

Q: Where are declared distances published?
A: In official AIPs, FAA Chart Supplements, airport diagrams, and sometimes commercial charts. Always use the operator’s published figures.

Q: Can pilots use the entire runway if the declared distance is less than the pavement length?
A: No. Only the published declared distances are legal and safe for performance calculations.

Q: How do declared distances impact flight operations?
A: They determine whether an aircraft can safely take off or land under given conditions. Ignoring them is a regulatory violation and a safety hazard.

Illustrative Example

Image: Diagram illustrating TORA, TODA, ASDA, LDA, clearway, stopway, and displaced threshold (Source: FAA).

Conclusion

Declared distances are a cornerstone of safe, standardized, and compliant airport and aircraft operations worldwide. Understanding and using them correctly is essential for every pilot, dispatcher, and airport operator.

Always consult the latest official publications for declared distances before every flight, and never exceed the published values in planning or operations.

For more information, consult:

• ICAO Annex 14 – Aerodromes
• FAA Advisory Circular 150/5300-13B
• Your country’s Aeronautical Information Publication (AIP)

If you have further questions or need specialized support with declared distances or airport planning, contact our experts .

Last updated: 2024